Time division multiplexed (TDM) telephone systems typically have a Central Processing Unit (CPU) controlling the TDM connections between port peripherals. This is accomplished typically be directly addressing an addressed or receiving peripheral in response to a transmitting or Source peripheral and routing the TDM pulse code modulation (PCM) words between the connected peripherals. That type of connection is on a random addressing basis and with the timing controlled by the immediate needs of the peripherals.
The disadvantage of that arrangement is the distributed processing required to control the addressing and the decoding and the status within each peripheral unit. Additionally, such devices require a sequential addressing either involving more addressing machinery or faster addressing machinery.